This page gives only an overview of this topic. For more information see the link at the bottom of this page

The Prostate Specific Antigen or PSA test is a blood test used to indicate the risk that prostate cancer is present.  PSA is a protein normally produced by the prostate but often seen at higher than normal levels when prostate cancer is present. 

Most doctors agree that men with a PSA greater than 4 ng/ml (nanogram per milliliter) should have further investigations. Less than half of them will ultimately be shown to have prostate cancer. This is because there are other conditions which can cause PSA to rise¹. They include benign prostate enlargement, prostatitis, infection and other causes.

Prostate cancer can also be present when PSA is below 4 ng/ml. About 15% men with PSA 4ng/ml or less had prostate cancer in one study ².

Because PSA slowly rises with age due to non-cancer reasons, some authorities say that normal thresholds should also increase with age. Normal ranges for age are shown in PHIP no 2.

Other PSA measures which can help tell prostate cancer from other causes are Free to total PSA and PSA velocity (rate of change).

Some doctors recommend using more than one measure to increase the accuracy of the estimate of your prostate cancer risk. This can be done using a nomogram - devices which base estimates of risk on the experience of many 1000s of patients.

One recent prostate cancer nomogram gives risk  of prostate cancer based on age, race, PSA level and rectal examination findings. It is available here.

Talk to your doctor to find out which of these measures are most relevant to you. Your best chance of detecting prostate cancer is with both a PSA test and a digital rectal examination.

Link

Medline Plus : http://www.nlm.nih.gov/medlineplus/ency/article/003346.htm#Normal Values

Studies quoted

1. Harris, R. and K.N. Lohr, Screening for prostate cancer: an update of the evidence for the U.S. Preventive Services Task Force. Annals of Internal Medicine. Online., 2002. 137(11): p. 917-29.
2. Thompson IM, Pauler DK, Goodman PJ, et al. Prevalence of prostate cancer among men with a prostate-specific antigen level < or =4.0 ng per milliliter. New England Journal of Medicine. 2004;350(22):2239-46.